The present invention relates to retrievable bridge plugs and related setting and retrieving tools and in particular to retrievable bridge plugs for placement in pressurized hydrocarbon wells to temporarily seal a portion of the well. The bridge plug has a selectively opened and closed through bore that allows pressure equalization before retrieval and permits well service tools to pass there through without requiring removal of the bridge plug. Improper setting of the bridge plug is prevented by a setting mechanism that is locked until located in the proper size tubing.
Bridge plugs are tools that are typically lowered into a cased oil or gas well. When set in position inside the casing, a bridge plug provides a seal to isolate pressure between two zones in the well. Retrievable bridge plugs are used during drilling and workover operations to provide a temporary separation of zones. When multilateral or multibore wells are drilled, bridge plugs are used to temporarily seal off the tubing set in the completed bores or laterals during servicing or completion of additional bores.
Typical bridge plugs are shown in U.S. Pat. No. 4,436,150 issued to Barker on Mar. 13, 1984; U.S. Pat. No. 4,898,239 issued to Rosenthal on Feb. 6, 1990; U.S. Pat. No. 5,058,684 issued to Winslow on Oct. 22, 1997; U.S. Pat. No. 5,727,632 issued to Richards on Mar. 17, 1998; U.S. Pat. No. 6,244,642 issued to Serafin et al. on Jun. 12, 2001. Baker sells a model xe2x80x9cGTxe2x80x9d LOK-SET Retrievable Bridge Plug and Model xe2x80x9cLTCxe2x80x9d Retrieving Head. Retrievable bridge plugs typically have anchor elements (slips or the like) and sealing elements. The anchor elements are used to grip the inside surface of a tubular member such as a well casing to prevent the set bridge plug from moving up or down. Note that as used herein, xe2x80x9cdownxe2x80x9d, xe2x80x9cdownwardxe2x80x9d, or xe2x80x9cdownholexe2x80x9d refer to the direction from the wellhead toward the producing zone regardless of whether the wellbore proceeds straight and directly downward from the surface. Up, upward, and uphole is in the reverse direction of downhole. xe2x80x9cSurfacexe2x80x9d refers either to the ground level or to the ocean floor, as applicable. The sealing elements engage the inside surface of the well casing to provide the requisite seal for the annulus defined between the bridge plug and the casing. Typically, the bridge plug is set in position by radially extending the anchor and the sealing elements to engage the well casing. To retrieve the bridge plug from the well casing, a retrieving tool is lowered down the casing to engage a retrieving latch, which, through a retrieving mechanism, retracts the anchor and the sealing elements, allowing the bridge plug to be pulled out of the well bore.
During well operations, a pressure differential across the plug often develops. It is desirable to equalize this pressure differential before the anchor and sealing elements are disengaged. Equalization prevents the loss of control over the bridge plug, wherein the tool may be blown up or down a well casing in response to the pressure differential. As exemplified by the prior art bridge plugs listed above, such equalization is typically effected through the opening of a bypass passage through the interior of the plug, prior to disengagement of the anchor and sealing elements.
However, a problem is encountered with these prior art devices in their inability to permit testing of well conditions in the completed bore. In these devices testing requires removal of the bridge plug.
With prior art retrievable bridge plugs dangerous situations can occur when setting is attempted in the incorrect location. The anchors and expandable seals of bridge plugs are designed to set in a narrow range of tubing sizes. When retrievable bridge plugs are to be set in tubing located in a lateral, it is essential that the bridge plug be located within the smaller lateral tubing liner before setting. Attempted setting short of the liner damages the tool and results in a defective seal off.
Bridge plugs having seals positioned between anchors causes the compressed seal elements to act as a compression spring. This spring force bears on the slip bodies pushing the carbide buttons on the slips deeper into the tubing. Releasing the slips requires pulling with enough force to actually rip the slip button out of the tubing wall. Typically, steeper slip angles and fewer buttons and slips are used to reduce the amount of force required to pull one set of slips loose. These solutions reduce the holding effectiveness of the slips.
When running the bridge plugs of the prior art in to the well, circulating ports in the inner mandrel are present to allow sufficient fluid bypass flow rates. These circulation ports weaken the inner mandrel and force flow into the interior of the mandrel.
According to the present invention, an improved retrievable bridge plug assembly and retrieving tool is provided. According to the bridge plug assembly of the present invention, an unobstructed straight central passageway extends through the plug and can be selectively opened and closed by the retrieving tool. When closed, the area below the bridge plug is isolated from the well above the plug. When open, pressure can be applied below the bridge plug and the pressure integrity below the bridge plug can be tested. In addition, this central passageway allows tool access to the area below the bridge plug assembly. For example, both xe2x80x9cpump throughxe2x80x9d and xe2x80x9cwire linexe2x80x9d tools can pass through the straight central opening. The packer assembly of the present invention utilizes a liner sensor above the slips and seals that prevents the bridge plug for trying to set until the sensor is inside the proper size tubing, preventing attempted setting outside the liner. According to the bridge plug of the present invention, the slips that resist movement are located below the seal elements. This protects the slips from debris and makes the slips easier to retrieve. The improved bridge plug of the present invention utilizes a flow path around the seal slip elements through a concentric bypass between the inner mandrel and the seal/ratchet/slips mandrel. Fluid enters through slots in the lower slip body, passes through slots in the seal/ratchet/slips mandrel and exits through holes in the bypass seal body. The concentric bypass eliminates the need for circulation ports and forces fluid to circulate around the bottom of the bridge plug and through any tail pipe attached to the bottom of the bridge plug.